Compensatory Energetic Relationships between Upstream Activators and the RNA Polymerase II General Transcription Machinery

Abstract

Activation of RNA polymerase II transcription in vivo and in vitro is synergistic with respect to increasing numbers of activator binding sites or increasing concentrations of activator. The Epstein-Barr virus ZEBRA protein manifests both forms of synergy during activation of genes involved in the viral lytic cycle. The synergy has an underlying mechanistic basis that we and others have proposed is founded largely on the energetic contributions of (i) upstream ZEBRA binding to its sites, (ii) the general pol II machinery binding to the core promoter, and (iii) interactions between ZEBRA and the general machinery. We hypothesize that these interactions form a network for which a minimum stability must be attained to activate transcription. One prediction of this model is that the energetic contributions should be reciprocal, such that a strong core promoter linked to a weak upstream promoter would be functionally analogous to a weak core linked to a strong upstream promoter. We tested this view by measuring the transcriptional response after systematically altering the upstream and core promoters. Our data provide strong qualitative support for this hypothesis and provide a theoretical basis for analyzing Epstein-Barr virus gene regulation.